1. Field of the Invention
The present invention relates to a solid state image sensing device in which Electromagnetic compatibility (referred to as EMC from here on) measures, i.e., Electromagnetic interference (referred to as EMI from here on) and Electromagnetic susceptibility (referred to as EMS from here on) measures are taken.
2. Description of Related Art
Most of solid state image sensing devices are constructed as a so-called multi-chip module in which a solid state image sensor and two or more integrated circuit chips are disposed on a printed wiring board, and are used for camcorder recording apparatus, digital cameras, camera-equipped personal digital assistants, camera-equipped mobile phones, and so on. Therefore, a downsizing of solid state image sensing devices has been required.
For example, a camera-equipped mobile phone has a housing having a very small mounting area and a very small mounting volume, in which processing circuits for processing an image signal, a voice signal, a data signal, etc., a control circuit for controlling these circuits, a communication circuit for converting the processed signals into electric waves and for transmitting them and receiving electric waves, a liquid-crystal-display circuit, and so on are mounted, and these circuits need to operate simultaneously. Electric waves emitted out of such a camera-equipped mobile phone may cause electromagnetic induction in each of the circuits mounted in the mobile phone, and this electromagnetic induction may cause the camera-equipped mobile phone to malfunction.
As a result of the malfunction, there cause signs of trouble, such as a striped pattern which appears in a picked-up image, distortion of the picked-up image, improper color reproduction of the picked-up image, and reduction in the signal-to-noise ratio of the picked-up image. In addition, there is a possibility that a passing through current noise peculiar to CMOS circuits, which has occurred in a digital circuit of the camera-equipped mobile phone flows into an image pickup processing circuit by way of power supply electric lines, and can reduce the signal-to-noise ratio of the picked-up image. Unnecessary radiation of electromagnetic waves may occur from the solid state image sensing device mounted in the mobile phone, and may induce other circuits mounted in the mobile phone and produce noises. As a result, such unnecessary radiation of electromagnetic waves from the solid state image sensing device may cause the other circuits mounted in the mobile phone to malfunction.
Therefore, EMC measures have to be taken in a prior art solid state image sensing device on which an integrated-circuit-chip module is mounted. For example, the integrated-circuit-chip module is implemented on a printed wiring board or package that is so designed that EMC measures are installed.
Concretely, the following techniques are used as the above-mentioned EMC measures. A method of shielding noise sources or parts which are easy to be influenced by noises, i.e., a method of shielding against electric fields, and a method of reducing the impedance of power supply electric lines so as to reduce changes in a voltage drop due to a current change, and, in order to prevent a signal that occurs in a circuit from entering other circuits via a power supply circuit, widening both a power supply electric line having a power supply potential and another power supply electric line having a ground potential (referred to as a pair of power supply electric lines from here on) which are formed on the printed wiring board, and arranging them in the form of a plane-shaped pattern. In addition, there has been provided another method (see patent reference 1) of forming a multilayer printed wiring board, forming clock signal electric lines in both layers which are located above and under a power supply layer or a ground layer, respectively, and forming grounded guard patterns on both sides of and in the vicinity of each of the clock signal electric lines.
In an integrated circuit chip mounted in such a printed wiring board or a packaged board in which EMC measures are taken, one electric line having a power supply potential and another electric line having a ground potential are not adjacent to each other in a plane, but are so arranged that they overlap in three dimensions, and an electrode pad for connecting with the electric line having a power supply potential and another electrode pad for connecting with the electric line having a ground potential are not arranged side by side along one side of the LSI chip (see patent reference 2). In a prior art packaged board, a power supply potential is supplied from an external lead, by way of a through hole, to a power supply conductor which is sandwiched by grounded conductors, and this power supply conductor is connected to a semiconductor chip by way of a through hole while the grounded conductors are connected to each other by way of a through hole (see patent reference 3).
Conventionally, in most cases, after a design stage in which a solid state image sensing device is contained in either a module or a package has been completed, examination of EMC measures is actually performed in a stage of mounting a printed wiring board on which the module or package containing the solid state image sensing device is disposed. Then, a measure of reducing the resistance of power supply electric lines as small as possible so as to reduce changes in the power supply voltage due to changes in the consumed electric current flowing through the solid state image sensing device, which occur while the solid state image sensing device operates, a measure of shielding a part of the circuit that needs to be running delicately from electromagnetic fields so as to shield electromagnetic induction from outside the solid state image sensing device, and a measure of shielding a part of the circuit that handles a high-frequency signal against electromagnetic fields so as to prevent electromagnetic waves from leaking to outside the solid state image sensing device are taken.
To be more specific, a measure of widening the power supply electric lines and a measure of enclosing a part of the circuitry of the solid state image sensing device with a metal plate are taken. As an alternative, a measure of forming interlayer electric lines in the form of a plane-shaped pattern in the multilayer printed wiring board, as well as a measure of widening the power supply electric lines and a measure of enclosing a part of the circuitry with a metal plate, are taken.
[Patent reference 1] Japanese patent application publication No. 2000-20573 (pp. 3 to 4 and FIGS. 3 and 5)
[Patent reference 2] Japanese patent application publication No. 2002-26272 (pp. 7 and FIG. 11)
[Patent reference 3] Japanese patent application publication No. 6-216272 (pp. 3 to 4 and FIG. 1)
As can be seen from the above description, a problem with a prior art solid state image sensing device constructed as above is that while EMC measures are not adequately taken in design stages and EMC measures are hardly installed in design stages for either a module or package in which a solid state image sensor is mounted, the widening of the power supply electric lines, which is carried out as EMC measures, causes an increase in the size of the solid state image sensor and the size of a printed wiring board on which the solid state image sensor is mounted, the enclosing of the solid state image sensor and other components with a shielding member, such as a metal plate, causes an increase in the sizes of those components, as well as an increase in the weights of the components. As a result, the EMC measures which are thus taken run counter to requests for reduction in the size and weight of the prior art solid state image sensing device provided with the solid state image sensor and so on. Another problem is that since additional material costs and additional manufacturing processes are needed for the EMC measures, the manufacturing cost is increased.